The year 1991 was a good one for rock music. It produced some of the best albums of all time, including “Blood Sugar Sex Magik” by Red Hot Chili Peppers, “Achtung Baby” by U2, “Out of Time” by R.E.M., “Ten” by Pearl Jam and “Metallica” by Metallica.

But none of them had the impact of Nirvana’s “Nevermind.” Not since “Meet The Beatles!” had there been such a seismic shift in pop culture. It was as if a demarcation line had been drawn between Baby Boomers and Generation X, and everything — music, film, fashion, even attitudes toward social conventions — changed forever.

“A whole new genre came out of it,” said Chris Brown, head of marketing for Bull Moose Music. “It redefined radio.”

This September marks the 20th anniversary of the release of “Nevermind,” and to mark the occasion, Universal Music is re-issuing it with a boatload of bonus material, including never-before-released demos, outtakes and videos, including the holy grail to Nirvana collectors: the original mixes by Butch Vig. It’s the first time the entire album has been remastered, and it was done right here in Portland by Bob Ludwig at Gateway Mastering.

Ludwig has worked on Nirvana material before, most notably the band’s third and final studio album, “In Utero,” in 1993. (Kurt Cobain fell asleep in front of Ludwig’s left speaker in the studio.)

And although Ludwig has worked with the biggest of the big in the music industry, working on “Nevermind” was a special treat. He handled the entire package, from the original album to the bonus tracks and a film of a Halloween 1991 concert at the Paramount Theatre in Seattle.

” ‘Nevermind’ sold more than 10 million copies, and it’s one of those cultural landmark records,” Ludwig said. “I was really happy that they asked me to master this.”

I had a chance to listen to some of the remastered tracks at Ludwig’s invitation earlier this week. The difference is phenomenal — the vocals are more crisp, the guitars more intense, the rhythm section thundering.

The bonus tracks are also revealing. The numerous demos and outtakes, which include studio banter between the band members, give listeners the chance to hear the songs’ progression from their raw genesis on a cassette tape recorder to the final product. And even on the final versions, the remastering has brought out sounds that were previously buried.

Surviving band members Krist Novoselic and Dave Grohl didn’t attend the remastering sessions, but were kept in the loop every step of the way, and were happy with the end result, Ludwig said.

“(Original producer) Butch Vig told me how delighted he was with it, and that really meant a lot to me,” he said.

The new edition of “Nevermind” is scheduled for a Sept. 27 release, and will be available as a two-CD deluxe edition, a four-CD super-deluxe edition with the Paramount Theatre concert on a bonus DVD, and a four-LP vinyl edition, as well as digital downloads. The Paramount Theatre film will also be available as a separate buy on DVD and Blu-ray.

Deputy Managing Editor Rod Harmon may be contacted at 791-6450 or at:

[email protected]